BMR Calculator for Weight Loss
Your BMR is the starting point for any weight loss plan. Here is how to turn a resting calorie number into a daily eating target — with a worked example, safe deficit ranges, and the mistakes that stall progress.
What BMR Means for Weight Loss
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — the energy required to keep your heart beating, lungs breathing, liver functioning, and every other organ running. It is not your daily calorie target; it is your floor.
To lose fat you need to eat below your TDEE (Total Daily Energy Expenditure) — which is your BMR multiplied by an activity factor that accounts for movement, exercise, and daily tasks. Eating below your BMR, not just below TDEE, is the danger zone where muscle loss accelerates and your metabolism adapts downward.
The practical implication: use your BMR as a reference point and your TDEE as the number you subtract your deficit from. The BMR calculator will show you both.
From BMR to Your Daily Calorie Target
- Calculate your BMR using the BMR calculator (Mifflin-St Jeor formula is recommended for most people)
- Multiply by your activity factor: sedentary ×1.2, lightly active ×1.375, moderately active ×1.55, very active ×1.725
- The result is your TDEE — the calories needed to maintain your current weight
- Subtract 250 kcal/day for slow loss (~0.25 kg/week), or 500 kcal/day for moderate loss (~0.5 kg/week)
- Eat at that target consistently for 3–4 weeks before evaluating and adjusting
Resist the urge to start with the largest deficit. A 250–500 kcal deficit is sustainable; a 1,000 kcal deficit is not for most people, and the rebound effect is well documented.
Worked Example
BMR (Mifflin-St Jeor female):
(10 × 75) + (6.25 × 165) − (5 × 28) − 161 = 750 + 1,031 − 140 − 161 = 1,480 kcal/day
TDEE (lightly active × 1.375): 1,480 × 1.375 = 2,035 kcal/day
Calorie targets:
Slow loss (250 kcal deficit): 1,785 kcal/day → ~0.25 kg/week
Moderate loss (500 kcal deficit): 1,535 kcal/day → ~0.5 kg/week
Do not eat below 1,480 kcal (BMR floor) for extended periods.
Safe Weekly Loss Rate
One kilogram of body fat contains approximately 7,700 kcal. The table below shows how deficit size translates into weekly loss and time to reach a 10 kg target.
| Daily deficit | Weekly loss | Time to lose 10 kg |
|---|---|---|
| 250 kcal | ~0.25 kg | ~40 weeks |
| 500 kcal | ~0.5 kg | ~20 weeks |
| 750 kcal | ~0.75 kg | ~13 weeks |
| 1,000 kcal | ~1 kg | ~10 weeks |
Deficits above 500 kcal/day are only sustainable short-term and carry a meaningfully higher risk of muscle loss, fatigue, and metabolic adaptation. The 500 kcal/day target is the widely accepted upper limit for sustainable fat loss.
Why Eating Below BMR Backfires
When calorie intake drops significantly below maintenance, the body responds by reducing NEAT (Non-Exercise Activity Thermogenesis) — the spontaneous movement and fidgeting that accounts for 100–300 kcal/day in most people. You unconsciously move less, stand less, and burn fewer calories without realising it.
This is the mechanism behind the well-documented Minnesota Starvation Experiment, in which participants on severe restriction experienced not only rapid weight loss but profound reductions in metabolic rate, muscle mass, and cognitive function — with the metabolic suppression persisting for months after the diet ended.
The fix is a moderate, consistent deficit paired with resistance training to preserve lean muscle mass. Muscle is metabolically active tissue — maintaining it keeps your BMR higher throughout the weight loss process and reduces the risk of rebound weight gain when you return to maintenance eating.
How Often to Recalculate
As you lose weight, your BMR falls — there is simply less body mass requiring energy maintenance. A 10 kg weight loss typically reduces BMR by 80–120 kcal/day. If you do not update your calorie target to reflect your new lower weight, your deficit narrows and weight loss stalls.
Recalculate your BMR and TDEE every 4–6 weeks or after every 5 kg lost. Always use your current weight, not your starting weight. It is also worth reassessing your activity multiplier — people who lose significant weight often become less active incidentally (less effort to move a lighter body), which can affect TDEE.
Enter your current weight, height, age, and sex into the yootils BMR calculator to get your BMR and all five TDEE activity levels instantly.
Open BMR Calculator →Also see: BMR vs TDEE Guide · Macro Calculator
Frequently Asked Questions
How many calories to lose 1 kg per week?
1 kg of fat ≈ 7,700 kcal, so a 1,100 kcal/day deficit is needed — aggressive for most people. A 500 kcal/day deficit gives ~0.5 kg/week and is considered the sustainable upper limit. Subtract your deficit from TDEE (not BMR) to set your daily target.
Can I eat below my BMR to lose weight faster?
Not recommended for extended periods. Your BMR is the calorie floor for organ function. Consistently eating below it triggers metabolic adaptation, muscle loss, and hormonal disruption. A 250–500 kcal deficit below TDEE is the safe range.
Why am I not losing weight in a calorie deficit?
Common causes: activity multiplier too high (overestimating TDEE), calorie tracking error (people underestimate intake by 20–40%), water retention masking fat loss, or metabolic adaptation. Track weight as a 7-day rolling average and reassess after 3 weeks.
How often should I recalculate my BMR?
Every 4–6 weeks or after losing ~5 kg. As weight drops, so does BMR — a 10 kg loss typically reduces it by 80–120 kcal/day. Using your starting weight instead of current weight is the most common cause of a weight loss plateau.
Evidence & Methodology
How This Page Is Grounded
Method
Uses estimated BMR, an activity factor and an explicitly stated calorie adjustment to illustrate a weight-loss planning target.
Important limitation: Energy needs and safe goals are individual; this is educational information, not a prescribed diet.
Primary Sources
Quality Checks
Worked BMR, TDEE and calorie-target arithmetic is checked against the calculator.
See how sources are selected and corrections are handled in our Editorial & Calculation Methodology, and which automated checks this page has to pass in How We Test.